1. Field of the Invention
The invention generally relates to textured multi-component yarns having increased elasticity and recovery, and processes for their production. More specifically, the invention relates to multi-component yarns having a polybutylene terephthalate component and a component of another thermoplastic material, and having good physical and aesthetic properties along with improved elasticity and recovery, and processes for their production.
2. Description of the Prior Art
Fabrics woven from synthetic yarns such as those made from textured polyethylene terephthalate (PET) are commonly used in many applications, due in part to their strength and durability. The types of yarns used are selected to achieve the desired properties for the intended end use. For example, air jet textured yarns are often utilized because of the ease with which they can be produced. One disadvantage of fabrics made from air jet textured PET yarns is that they generally have limited elasticity/recovery capability. This becomes particularly apparent when the fabric woven from such yarns is used to cover an irregularly-shaped article. For example, when fabrics woven from conventional bulk PET yarns are to be used to cover items such as automotive seating, it can be difficult to get a close fit of the fabric without extensive labor input to custom-fit the fabric to the seat. As a result, such fabrics can tend to pucker and gap, thereby causing a reduced quality appearance. Furthermore, since such seating is generally cushioned, it often results that the fabric is worn undesirably as a result of its inability to stretch and recover when the cushioned seating is compressed, as when someone sits on it.
Attempts have been made to increase the elasticity of air jet textured PET yarns used in woven fabrics; however, such attempts typically have involved increasing the amount of shrinkage in the yarns, since an increase in elasticity and recovery generally accompanies an increase in shrinkage. However, increasing the shrinkage in the yarn end product can be particularly difficult when it is desired that the yarns are to be colored. In processes where the PET yarns are package dyed, the heating stage of the dye process tends to virtually eliminate the ability of the yarns to shrink. As a result, the package-dyed air jet textured PET yarns generally have little to no elasticity or recovery capability.
The other option generally available for obtaining dyed PET yarns having some elasticity is by solution dyeing the yarns (i.e., introducing polymer pigments or insoluble dyes into the polymer melt or spinning solution prior to extrusion), and false twist texturing them, since false twisting generally produces yarns having high levels of shrinkage. Because the color is therefore inherent in the yarn prior to texturizing, the elastic properties of the yarn can be retained. However, because the yarns retain a relatively high level of shrinkage, when fabrics woven from the solution-dyed false-twist textured PET yarns are subjected to heat during fabric finishing processes, they have a tendency to shrink, leading to significant yield losses and quality problems in the end product.
Another attempt for increasing the stretchability of PET fibers is described in U.S. Pat. No. 4,755,336 to Deeg, et al. This patent describes a process for melt spinning a blend of about 5 to 25% by weight of polyethylene terephthalate (PET) with polybutylene terephthalate (PBT), to produce a yarn having increased stretchability. As described in the patent, the fibers are drawn at an elevated temperature following extrusion to induce a specific form of crystal. The yarns are then subjected to a heat relaxation treatment which changes the crystal form of the polybutylene terephthalate to add shrinkage, thereby causing the fibers to have an increased degree of stretchability. Because the polybutylene terephthalate and polyethylene terephthalate are mixed while in their molten form, the resulting yarns would have properties which are essentially a compromise between the properties of the two material inputs, and thus which would differ from the physical and aesthetic properties of the all-PET yarns. In addition, because the elasticity is increased by increasing yarn shrinkage, the problem of yield loss would still exist when the yarns are converted to a finished product. Furthermore, the large majority of the material input is PBT, and because PBT is generally more expensive than PET, the yarns discussed in the Deeg, et al. patent would tend to be significantly more expensive than the all-PET yarns.
Thus, a need exists for yarns which can be used in the production of woven fabrics which have a good degree of elasticity and recovery, along with good physical and aesthetic properties. In addition, a need exists for yarns which can be used in the production of woven fabrics having increased elasticity and recovery, at set levels of shrinkage.